Six more bodies were recovered from the Atlantic Ocean where an Air France jet crashed, as the race to find the black boxes and gather key evidence from human remains and debris gained urgency.

On the coast, investigators examined corpses and received the first wreckage: two plane seats, oxygen masks, water bottles, and several structural pieces, some no bigger than a man’s hand.

Almost two weeks after the crash, Brazil’s military said the search was becoming increasingly difficult and a tentative June 25 date for halting efforts had been set.

From Monday, officials will meet every two days to evaluate when to stop the search, depending on whether they are still finding bodies or debris.

The black boxes – whose emergency beacons begin to fade after 30 days – along with debris and bodies from the jet, all contain crucial clues on how and why Air France Flight 447 went down en route from Rio de Janeiro to Paris with 228 on board, including five Britons, on May 31.

William Waldock, who teaches air crash investigation at Embry-Riddle Aeronautical University in Prescott, Arizona, said the ability for a body to float in water and remain visible to searchers depended highly on water temperatures and sea life in the area.

According to the Brazilian military, the water temperature in the areas they are looking is averaging about 82 degrees (28 degrees Celsius) – warm water that speeds up the process of a body surfacing, floating, and then sinking once again, Mr Waldock said.

“At this point, it’s not really surprising you are hearing them (the Brazilian military) talking about an end to the search,” he said.

In water temperatures like those in the search area, Mr Waldock said an intact body could probably float for two or three weeks – Air France Flight 447 went down May 31 with 228 on board. Those warm waters also mean there is a lot of marine life in the area and “they’ll break a body down faster”.

A body, once torn open, would quickly sink, he noted.

Medical authorities examining the 16 bodies already brought on to land in Recife have refused to release information about the state of the corpses.

Meanwhile, military ships and planes continued to struggle in worsening weather to find more bodies and debris.

The most important piece recovered is the virtually intact vertical stabiliser, which could give the French investigative agency BEA solid clues about what prompted the crash.

The plane’s black boxes – perhaps the best hope of definitively learning what went wrong – remain elusive. A French nuclear submarine is scouring the search area in the hope of hearing pings from the boxes’ emergency beacons. The first of two US locator listening devices will arrive tomorrow.

So far, there is no evidence of an explosion or terrorist act, but a number of clues that describe systemic failures on the plane.

A burst of 24 automatic messages sent during its final minutes of flight show the autopilot was not on, but it was not clear if it was switched off by the pilots or had stopped working due to conflicting airspeed readings, perhaps caused by iced-over speed sensors.

If the black boxes are not found, the cause could still be determined – though with much more effort.

Without any other solid clues, investigators have focused on the possibility that external speed monitors iced over and gave false readings to the plane’s computers.

Air France ordered these Pitot tubes replaced on the long-range Airbus planes on April 27 after pilots noted a loss of airspeed data in a few flights on Airbus A330 and A340 models.